Perspiration or sweat production is a completely natural physiological process made by the animal body and many people sweat more than they realise. It may come as a surprise to most people that the average person produces ½ to 1 liter sweat every day.
Human sweat itself is largely odorless. The principal cause of body odor are bacteria thriving in hot, humid environments such as the human underarm, which has a high density of sweat glands and is relatively occluded, which may be caused by an excessive production of sweat. The armpits are among the consistently warmest areas on the surface of the human body, and sweat glands provide moisture. Armpit hair adds to the odor because of the increased surface area.
The odor is seen as negative in most cultures, hence many people have a desire to eliminate or suppress it. One obvious way to reduce odor is to remove some, or all, of the underarm hair. Another way, or an additional way, to reduce the odor and the concentrated sweat production is to temporary plug the sweat duct causing the flow of sweat to the skin's surface to stop or to be reduced. This temporary plug may be provided by the use of an antiperspirant.
Antiperspirants are formulations having an aluminum-based compound as their main “active” ingredient, which can be any number of compounds within an established concentration and dosage form. The active ingredient gives antiperspirants their sweat-blocking ability by forming a temporary plug within the sweat duct that stops the flow of sweat to the skin's surface.
Thus, antiperspirant formulations may prevent odor and reduce sweat produced by the body.
EP 0 386 018 describes an efficient antiperspirant composition, wherein a metal salt is combined with a buffer salt suspended in alcohol. However, this composition has the drawback of developing sedimentation of the suspended particles during storage. This sedimentation causes an inhomogeneous dosing of the antiperspirant and leakage of the composition from the roller-ball of the device.
During production of products, it may be necessary to mix two or more types of liquid which as such are not mixable. To overcome this, liquids may be mixed in an emulsion where a temporary or permanent dispersion of an oil or another hydrophobic material in an aqueous solution, or vice versa, forming an oil-in-water emulsion or a water-in-oil emulsion. Generally, such oil-in-water or water-in-oil emulsions are capable of providing a stable solution.
Thus, it is suggested to provide a different system, such as an alcohol-in-oil type emulsion. This alcohol-in-oil type emulsion is not an emulsion as such because of the lack of water. However, it is a mixture of two types of liquid which as such are not mixable, namely a lower alcohol and an oil. However, it is established knowledge in the art that such kind of alcohol-in-oil type emulsions containing high levels of particles, e.g. multivalent metal ions, are considered as being unstable.
To improve the chemical stability of suspended particles that will release hydrochloric acid in presence of water, there is a need for a water-free composition, such as a alcohol-in-oil type emulsion. At the same time the water-free emulsion must be stable even in presence of a high level of electrolytes to provides a homogeneous distribution of the suspended particles.